1. Field of the Invention
The present invention relates to a boat provided with a connection structure arranged to connect a coupling via an intermediate member to a rear end portion of an output shaft extending rearward from an engine disposed in a hull for outputting a motive power of the engine.
2. Description of the Related Art
Conventionally, for example, there is a boat that ejects water suctioned from a bottom of the boat in the rear direction of a stern by operation of a jet pump so as to travel on water. An engine is disposed in a central portion of a hull of such a boat. A crankshaft (output shaft) extends toward the rear direction from the engine such that a rear end portion of the crankshaft is connected to a pump drive shaft of the jet pump via a coupling. An impeller is connected to the pump drive shaft. Accordingly, a rotational force of the crankshaft by operation of the engine is transmitted to the impeller, and thus the impeller rotates. Consequently, a propulsive force is generated by the boat.
However, an intake port of the jet pump of the boat may be exposed to air and suction air during traveling. Therefore, a load applied to the impeller is temporarily reduced. As a result, the load applied on an impeller shaft and a crankshaft easily varies. Therefore, when the crankshaft and the coupling are directly connected, a length of the crankshaft becomes long. Then, flexure is easily generated in the crankshaft by the load variation described above. As a result, the durability of the crankshaft is decreased. Accordingly, a boat is provided with a connection structure that connects a rear end portion of the crankshaft and the coupling via an intermediate member (see JP-A-2003-26093, for example).
In this boat, the connection structure is provided with a crankshaft (output shaft), an output shaft (a separate shaft from the output shaft), a connecting pipe (an intermediate member), and a coupling. A spline is provided on a rear end of an outer circumferential surface of the crankshaft and a front end of an outer circumferential surface of the output shaft. Further, a spline is provided on an inner circumferential surface of the connecting pipe and is engaged with the spline of the crankshaft and the spline of the output shaft, respectively. As these splines are engaged, the crankshaft and the output shaft are connected via the connecting pipe. In addition, splines are also provided on a rear end of the outer circumferential surface of the output shaft and on the inner circumferential surface of the coupling and can be engaged with each other. As these splines are engaged, the output shaft and the coupling are connected.
However, although each movement in the rotational direction of the output shaft in relation to the crankshaft and of the coupling in relation to the output shaft can be restricted by engagement between the splines in the conventional boat described above, movement in the axial direction cannot be restricted. Accordingly, a bolt is inserted in the output shaft from the rear end of the output shaft, and a screw on an end thereof is screwed together with a screw provided on an inner surface of the crankshaft to prevent the output shaft from moving in the axial direction in relation to the crankshaft. However, even this construction cannot prevent the coupling from moving in the axial direction in relation to the output shaft which generates a positional displacement. In addition, as the coupling moves in relation to the output shaft, a loss is generated in the drive force transmitted from the crankshaft to the coupling. Moreover, because spline processing is time-consuming, the processing time and processing cost are increased.